Evaluation of thermal conductivity and flexural strength properties of poly(methyl methacrylate) denture base material reinforced with different fillers

Effect of titanium dioxide and zirconium dioxide nanoparticle incorporation on the thermal conductivity of heat-activated polymethylmethacrylate denture base resins: An in vitro experimental study

AIM

The aim is to determine thermal conduction by heat-activated polymethylmethacrylate (PMMA) infiltrated with 1 weight% Titanium Dioxide (TiO2) and 1 weight% Zirconium Dioxide (ZrO2) nanoparticles and to compare with that of conventional PMMA.

STUDY SETTING AND DESIGN

In vitro experimental study.

MATERIALS AND METHODS

Eighteen disc shaped specimens with a thickness of 5 mm and diameter of 50 mm, were fabricated and grouped according to the material used: Group B1 (resin infiltrated with 1 weight% TiO2), Group B2 (resin infiltrated with 1 weight% ZrO2), and Control Group B3 (heat-activated conventional PMMA resin). Disc-shaped specimens were analyzed for thermal conductivity using "modified guarded hot plate apparatus" in the thermal lab of the Indian Space Research Organisation.

STATISTICAL ANALYSIS USED

One-way ANOVA followed by Tukey's post hoc test was used to compare the arithmetic means of all three groups.

RESULTS

A statistically significant difference was noted among all three groups. Group B2 had the maximum thermal conductivity, followed by Group B1. Thermal conductivity was the least for Group B3. A post hoc comparison revealed that the difference was significant between Group B2 and Group B3.

CONCLUSION

Nano ZrO2 addition in PMMA increased its thermal conductivity. There is evidence that it improves its mechanical properties as well. Hence, Nano ZrO2 addition in PMMA is highly recommended. Nano TiO2 addition in PMMA did not provide any significant advantage in terms of thermal conductivity, but its addition in PMMA is justified because of its mechanical and antimicrobial properties.

Evaluation of the flexural strength of orthodontic acrylic resin incorporated with propolis nanoparticles: an in vitro study

AIM

Nanopropolis has become the subject of interest in medicine and dentistry as a natural product due to its outstanding properties, particularly antimicrobial activity. This study aimed at investigating the effect of nanopropolis on flexural strength of polymethyl methacrylate (PMMA).

Different Polymers for the Base of Removable Dentures? Part I: A Narrative Review of Mechanical and Physical Properties

Even before considering their introduction into the mouth, the choice of materials for the optimization of the prosthesis depends on specific parameters such as their biocompatibility, solidity, resistance, and longevity. In the first part of this two-part review, we approach the various mechanical characteristics that affect this choice, which are closely related to the manufacturing process. Among the materials currently available, it is mainly polymers that are suitable for this use in this field. Historically, the most widely used polymer has been polymethyl methacrylate (PMMA), but more recently, polyamides (nylon) and polyether ether ketone (PEEK) have provided interesting advantages. The incorporation of certain molecules into these polymers will lead to modifications aimed at improving the mechanical properties of the prosthetic bases. In the second part of the review, the safety aspects of prostheses in the oral ecosystem (fragility of the undercuts of soft/hard tissues, neutral pH of saliva, and stability of the microbiota) are addressed. The microbial colonization of the prosthesis, in relation to the composition of the material used and its surface conditions (roughness, hydrophilicity), is of primary importance. Whatever the material and manufacturing process chosen, the coating or finishes dependent on the surface condition remain essential (polishing, non-stick coating) for limiting microbial colonization. The objective of this narrative review is to compile an inventory of the mechanical and physical properties as well as the clinical conditions likely to guide the choice between polymers for the base of removable prostheses.

Material extrusion of thermoplastic acrylic for intraoral devices: Technical feasibility and evaluation

With global demand for 3D printed medical devices on the rise, the search for safer, inexpensive, and sustainable methods is timely. Herein, we assessed the practicality of the material extrusion process for acrylic denture bases of which successful outcomes can be extended to implant surgical guides, orthodontic splints, impression trays, record bases and obturators for cleft palates or other maxillary defects. Representative materials comprising denture prototypes and test samples were designed and built with in-house polymethylmethacrylate filaments using varying print directions (PDs), layer heights (LHs) and reinforcements (RFs) with short glass fiber. The study undertook a comprehensive evaluation of the materials to determine their flexural, fracture, and thermal properties. Additional analyses for tensile and compressive properties, chemical composition, residual monomer, and surface roughness (Ra) were completed for parts with optimum parameters. Micrographic analysis of the acrylic composites revealed adequate fiber-matrix compatibility and predictably, their mechanical properties improved simultaneously with RFs and decreased LHs. Fiber reinforcement also improved the overall thermal conductivity of the materials. Ra, on the other hand, improved visibly with decreased RFs and LHs and the prototypes were effortlessly polished and characterized with veneering composites to mimic gingival tissues. In terms of chemical stability, the residual methyl methacrylate monomer contents are well below standards threshold for biological reactions. Notably, 5 vol% acrylic composites built with 0.05 mm LH in 0° on z-axis produced optimum properties that are superior to those of conventional acrylic, milled acrylic and 3D printed photopolymers. Finite element modeling successfully replicated the tensile properties of the prototypes. It may well be argued that the material extrusion process is cost-effective; however, the speed of manufacturing could be longer than that of established methods. Although the mean Ra is within an acceptable range, mandatory manual finishing and aesthetic pigmentation are required for long-term intraoral use. At a proof-of-concept level, it is evident that the material extrusion process can be applied to build inexpensive, safe, and robust thermoplastic acrylic devices. The broad outcomes of this novel study are equally worthy of academic reflection, and further translation to the clinic.

A Comparative Evaluation of Flexural and Impact Strength of Polymethyl Methacrylate (PMMA) Reinforced With Graphene and Multi-Walled Carbon Nanotubes: An In Vitro Study

Background and objective Low flexural strength (FS) and impact strength (IS) are major drawbacks in removable prostheses made from polymethyl methacrylate (PMMA). Attempts to enhance the strength and longevity of these prostheses have been of keen interest among researchers. Nanofillers are new and advanced reinforcements that can chemically modify PMMA. Graphene and multi-walled carbon nanotubes (MWCNTs) were used in this study to evaluate FS and IS when added to polymer and monomer individually. Method Four groups were created based on the addition of nanofillers: no nanofillers - control; 0.5% by weight of graphene; 0.5% by weight of MWCNT; and 0.25% by weight of both. These groups were further subdivided into two according to the nanofiller being added to polymer and monomer each. The samples were then subjected to a 3-point bending test to assess FS, and an Izod impact tester was used to test IS. Results Decreased FS and FS were seen in all groups with the addition of nanofillers in the polymer (p<0.001). With the addition of nanofillers in monomer, increased FS and IS were seen in groups with MWCNTs whereas a decrease was seen with the addition of graphene (p<0.001). Conclusion Nanofillers should be added to the monomer of heat-cure PMMA instead of polymer; 0.5% by weight of MWCNT has shown the highest FS and IS when added to the monomer.

A Review of the Application of Natural and Synthetic Scaffolds in Bone Regeneration

The management of bone defects is complicated by the presence of clinical conditions, such as critical-sized defects created by high-energy trauma, tumour resection, infection, and skeletal abnormalities, whereby the bone regeneration capacity is compromised. A bone scaffold is a three-dimensional structure matrix serving as a template to be implanted into the defects to promote vascularisation, growth factor recruitment, osteogenesis, osteoconduction, and mechanical support. This review aims to summarise the types and applications of natural and synthetic scaffolds currently adopted in bone tissue engineering. The merits and caveats of natural and synthetic scaffolds will be discussed. A naturally derived bone scaffold offers a microenvironment closer to in vivo conditions after decellularisation and demineralisation, exhibiting excellent bioactivity, biocompatibility, and osteogenic properties. Meanwhile, an artificially produced bone scaffold allows for scalability and consistency with minimal risk of disease transmission. The combination of different materials to form scaffolds, along with bone cell seeding, biochemical cue incorporation, and bioactive molecule functionalisation, can provide additional or improved scaffold properties, allowing for a faster bone repair rate in bone injuries. This is the direction for future research in the field of bone growth and repair.

Advanced materials and technologies for oral diseases

Oral disease, as a class of diseases with very high morbidity, brings great physical and mental damage to people worldwide. The increasing burden and strain on individuals and society make oral diseases an urgent global health problem. Since the treatment of almost all oral diseases relies on materials, the rapid development of advanced materials and technologies has also promoted innovations in the treatment methods and strategies of oral diseases. In this review, we systematically summarized the application strategies in advanced materials and technologies for oral diseases according to the etiology of the diseases and the comparison of new and old materials. Finally, the challenges and directions of future development for advanced materials and technologies in the treatment of oral diseases were refined. This review will guide the fundamental research and clinical translation of oral diseases for practitioners of oral medicine.

A Comparison of the Surface and Mechanical Properties of 3D Printable Denture-Base Resin Material and Conventional Polymethylmethacrylate (PMMA)

PURPOSE

To study the surface and mechanical properties of 3D printed denture-base resin materials and compare them with conventional heat-cured polymethylmethacrylate (PMMA).

MATERIALS AND METHODS

Three brands of 3D printed denture-base resin materials and one conventional heat-cured PMMA were tested in this study: NextDent 3D printed resin, Dentona 3D printed resin, ASIGA 3D printed resin, and Meliodent conventional PMMA. Sixty specimens (25 × 25 × 3 mm) were fabricated (n=15 per group) to perform the following tests: wettability, surface roughness, and microhardness. One hundred twenty specimens (65 × 10 × 3 mm) were fabricated (n=30 per group) and stored in distilled water at (37 ±1°C) for 7 days. Specimens (N = 15) in each group were subjected to the three-point bending test and impact strength test, employing the Charpy configuration on un-notched specimens. The morphology of the fractured specimens was studied under scanning electron microscope (SEM). Statistical analysis was performed using one-way ANOVA and Tukey-pairwise multiple comparisons with 95% confidence interval. P-values of ≤0.05 were considered significant.

RESULTS

The conventional heat-cured specimens demonstrated the highest means of surface roughness (0.23 ± 0.07 μm), Vickers hardness number (18.11 ±0.65) and flexural strength (92.44 ±7.91 MPa), and the lowest mean of contact angle (66.71° ±3.38°). ASIGA group showed the highest mean of contact angle (73.44° ±2.74°) and the lowest mean of surface roughness (0.19 ±0.03 μm). The highest mean of impact strength was recorded in the Dentona group (17.98 ±1.76 kg/m² ). NextDent specimens showed the lowest means of Vickers hardness number (16.20 ±0.93), flexural strength (74.89 ±8.44 MPa), impact strength (15.20 ±0.69 kg/m² ), and recorded the highest mean of bending modulus (2,115.80 ±178.95 MPa).

CONCLUSIONS

3D printed resin exhibited noticeable differences in surface and mechanical properties between different brands and with conventional heat-polymerized PMMA.

Mechanical Properties of Polymethyl Methacrylate as Denture Base Material: Heat-Polymerized vs. 3D-Printed-Systematic Review and Meta-Analysis of In Vitro Studies

The synergy between dentistry and informatics has allowed the emergence of new technologies, specifically 3D printing, which has led to the development of new materials. The aim of this research was to compare the mechanical properties of dental base resins for 3D printing with conventional ones. This systematic review was developed using the PRISMA guidelines, and the electronic literature search was performed with the PubMed/MEDLINE, Web of Science-MEDLINE and EMBASE databases, until 30 April 2022. Two researchers selected the studies independently, and thus eight articles were found eligible for analysis. A meta-analysis was developed to estimate flexural strength. The Cohen's kappa corresponding to this review was 1.00, and the risk assessment was considered low for the included studies. The 3D printing resin presented lower values of flexural strength and hardness compared with the heat-cured resin. Regarding impact strength, a lower value was recorded for the heat-cured resin compared with the 3D printing resin. Three-dimensional printing resins are viable materials for making prosthetic bases but need further clinical research.

PMMA-Based Nanocomposites for Odontology Applications: A State-of-the-Art

Polymethyl methacrylate (PMMA), a well-known polymer of the methacrylate family, is extensively used in biomedicine, particularly in odontological applications including artificial teeth, dentures and denture bases, obturators, provisional or permanent crowns, and so forth. The exceptional PMMA properties, including aesthetics, inexpensiveness, simple manipulation, low density, and adjustable mechanical properties, make it a perfect candidate in the field of dentistry. However, it presents some deficiencies, including weakness regarding hydrolytic degradation, poor fracture toughness, and a lack of antibacterial activity. To further enhance its properties and solve these drawbacks, different approaches can be performed, including the incorporation of nanofillers. In this regard, different types of metallic nanoparticles, metal oxide nanofillers, and carbon-based nanomaterials have been recently integrated into PMMA matrices with the aim to reduce water absorption and improve their performance, namely their thermal and flexural properties. In this review, recent studies regarding the development of PMMA-based nanocomposites for odontology applications are summarized and future perspectives are highlighted.

Characterization of various acrylate based artificial teeth for denture fabrication

Acrylic resins-based artificial teeth are frequently used for the fabrication of dentures has and contribute a very strong share in the global market. However, the scientific literature reporting the comparative analysis data of various artificial teeth is scarce. Focusing on that, the present study investigated various types of commercially available artificial teeth, composed of polymethyl methacrylate (PMMA). Artificial teeth are characterized for chemical analysis, morphological features, thermal analysis, and mechanical properties (surface hardness, compressive strength). Different types of artificial teeth showed distinct mechanical (compression strength, Vickers hardness) and thermal properties (thermal gravimetric analysis) which may be attributed to the difference in the content of PMMA and type and quantity of different fillers in their composition. Thermogravimetric analysis (TGA) results exhibited that vinyl end groups of PMMA degraded above 200 °C, whereas 340-400 °C maximum degradation temperature was measured by differential thermal analysis (DTA) for all samples. Crisma brand showed the highest compressive strength and young modulus (88.6 MPa and 1654 MPa) while the lowest value of Vickers hardness was demonstrated by Pigeon and Vital brands. Scanning electron microscope (SEM) photographs showed that Crisma, Pigeon, and Vital exhibited characteristics of a brittle fracture; however, Artis and Well bite brands contained elongated voids on their surfaces. According to the mechanical analysis and SEM data, Well bite teeth showed a significantly higher mechanical strength compared to other groups. However, no considerable difference was observed in Vickers hardness of all groups. Graphical abstract.

Influence of Reinforcing Agents on the Mechanical Properties of Denture Base Resin: A Systematic Review

Knowledge about the influence of fillers in denture base resin is vague. This systematic review aimed to report the reinforcing effect of fillers on the mechanical properties of denture base resin by following PRISMA guidelines. Two electronic databases (Pubmed/Medline & Web of Science) were searched for articles using the keywords: fibers in denture base, fillers in denture base, and reinforcement of denture base. Laboratory studies complying with the inclusion criteria were reviewed according to the set protocol. The established focus question was: "Do reinforcing fillers positively influence the mechanical properties of polymethyl methacrylate (PMMA) heat polymerized denture base material?" A total of twenty-nine relevant papers qualified for final inclusion. Of these, 24 were determined to have a moderate risk of bias. Micron or nano-sized metal/metal oxides particles and glass fibers were the frequently used reinforcing agents. The trend of evaluating fractural strength (FS) was common. Most of the studies limited the use of reinforcing agents up to 5 wt.%. FS, fracture toughness (FT), and impact strength (IS) tend to increase if the fillers are chemically bonded and well-dispersed in denture base resin. Though fillers with a higher elastic modulus increase the hardness of the reinforced denture base resin, they compromise other mechanical properties. Well-dispersed lower filler loading PMMA denture base resin can enhance the FS, FT, and other related mechanical properties.

Flexural Strength and Hardness of Filler-Reinforced PMMA Targeted for Denture Base Application

The aim of this work was to evaluate the flexural strength and surface hardness of heat-cured Polymethyl methacrylate (PMMA) modified by the addition of ZrO₂ nanoparticles, TiO₂ nanoparticles, and E-glass fibre at different wt.% concentrations. Specimens were fabricated and separated into four groups (n = 10) to measure both flexural strength and surface hardness. Group C was the control group. The specimens in the remaining three groups differed according to the ratio of filler to weight of PMMA resin (1.5%, 3%, 5%, and 7%). A three-point bending test was performed to determine the flexural strength, while the surface hardness was measured using the Vickers hardness. Scanning Electron Microscope (SEM) was employed to observe the fractured surface of the specimens. The flexural strength was significantly improved in the groups filled with 3 wt.% ZrO₂ and 5 and 7 wt.% E-glass fibre in comparison to Group C. All the groups displayed a significantly higher surface hardness than Group C, with the exception of the 1.5% TiO₂ and 1.5% ZrO₂ groups. The optimal filler concentrations to enhance the flexural strength of PMMA resin were between 3–5% ZrO₂, 1.5% TiO₂, and 3–7% E-glass fibre. Furthermore, for all composites, a filler concentration of 3 wt.% and above would significantly improve hardness.

Effect of titanium dioxide nanoparticle reinforcement on flexural strength of denture base resin: A systematic review and meta-analysis

The study was designed to assess the change in flexural strength of unmodified heat cure denture base polymer resin on reinforcement with titanium dioxide nanoparticles in different concentrations. In vitro, randomized control trials reporting flexural strength of titanium dioxide nanoparticle reinforced resin were selected. The review was formulated based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses- Protocol (PRISMA-P) guidelines. Quality assessment was performed according to Consolidated Standards Of Reporting Trials (CONSORT) guidelines and risk of bias Cochrane tool. Six articles in the category of 1%, 3%, 5% weight fractions of titanium dioxide nanoparticles were subjected to a meta-analysis. A meta-analysis was performed using random-effects at a 95% confidence interval. Within the limitations of the study, it can be assumed that there is no precise conformity on the ideal titanium dioxide nanoparticle concentration required to improve the flexural strength of the polymer. Stringent use of standard ISO guidelines may help in obtaining consistent results.

Prosthodontic Applications of Polymethyl Methacrylate (PMMA): An Update

A wide range of polymers are commonly used for various applications in prosthodontics. Polymethyl methacrylate (PMMA) is commonly used for prosthetic dental applications, including the fabrication of artificial teeth, denture bases, dentures, obturators, orthodontic retainers, temporary or provisional crowns, and for the repair of dental prostheses. Additional dental applications of PMMA include occlusal splints, printed or milled casts, dies for treatment planning, and the embedding of tooth specimens for research purposes. The unique properties of PMMA, such as its low density, aesthetics, cost-effectiveness, ease of manipulation, and tailorable physical and mechanical properties, make it a suitable and popular biomaterial for these dental applications. To further improve the properties (thermal properties, water sorption, solubility, impact strength, flexural strength) of PMMA, several chemical modifications and mechanical reinforcement techniques using various types of fibers, nanoparticles, and nanotubes have been reported recently. The present article comprehensively reviews various aspects and properties of PMMA biomaterials, mainly for prosthodontic applications. In addition, recent updates and modifications to enhance the physical and mechanical properties of PMMA are also discussed.

Mechanical properties of new denture base material modified with gold nanoparticles

PURPOSE

Poly(methyl methacrylate) (PMMA) is the most commonly used material in the production of dental prostheses, and its application is often accompanied by the formation of biofilm. The aim of this work was the preparation of a PMMA/gold nanoparticles (AuNps) composite to improve the antimicrobial properties of heat-polymerised PMMA. The AuNPs were synthesised from gold (III) acetate by Ultrasonic Spray Pyrolysis (USP).In the present study, flexural strength and elastic modulus were investigated, as well as thermal conductivity, density and hardness of the PMMA/AuNps` nanocomposite, with different concentrations of AuNps. Flexural strength and elastic modulus were measured using a three-point bending test, and surface hardness was evaluated using the Vickers hardness test. The thermal conductivity of the samples was measured using the Transient Plane Source (TPS) technique. Density was determined by the pycnometry procedure. Statistical analysis was conducted on the data obtained from the experiments.

RESULTS

The flexural strength and elastic modulus of AuNps/PMMA nanocomposites decreased for all groups containing AuNps. Thermal conductivity and density increased in all groups containing AuNps compared to the control group, but it was not significant in all groups. Vickers hardness values increased significantly with an increase in AuNps` content, with the highest value 21.45 HV obtained at 0.74 wt% of AuNps. Statistical analysis was performed by means of the SPSS 19 software package.

CONCLUSIONS

Incorporation of AuNps into heat-polymerised PMMA resin led to decrease of the flexural strength and elastic modulus. At the same time, the density, thermal conductivity and hardness increased.

Chemical Modification of Cellulose Microfibres to Reinforce Poly(methyl methacrylate) Used for Dental Application

The mechanical properties of dental acrylic resins have to be improved in the case of a thin denture plate. This can be achieved by cellulose addition, playing the role of active filler. But to provide the excellent dispersion of cellulose microfibres within the hydrophobic polymer matrix, its surface has to be modified. Cellulose microfibres with average length from 8 to 30 μm were modified with octyltriethoxysilane and (3-methacryloxypropyl)methyldimethoxysilane. The latter also participated in the polymerisation reaction of methyl methacrylate. Dental composites were prepared following the general procedure provided by the supplier. The successful modification of the microfibres led to the improved compatibility of the cellulose and poly(methyl methacrylate). The fibres after modification were uniformly distributed within the matrix, resulting in the improved mechanical performance of obtained materials. Cellulose microfibres are good candidates for the dental materials to be used as the active filler. The simple and straightforward approach for the cellulose modifications with silanes provides good potential for its future practical application.

Effect of adding TiO2 nanoparticles on the SEM morphology and mechanical properties of conventional heat-cured acrylic resin

Background. The current study evaluated the compressive, flexural and impact strengths of heat-cured acrylic resins reinforced by TiO₂ nanoparticles (NPs).

Methods. TiO₂ NPs were provided and characterized using scanning electron microscopy (SEM) to determine their morphology and crystalline structure. For three mechanical tests, 12 acrylic resin groups (n=9), totaling 108 specimens, were prepared using a special mold for each test, with TiO₂ nanoparticle contents of 0, 0.5, 1 or 2 wt% in different groups. After curing, the compressive, flexural and impact strengths of the specimens were examined according to ISO 1567.

Results. In the SEM and XRD study of TiO2 NPs, anatase was identified as the major crystalline phase followed by rutile (average particle size: 20.4 nm). SEM images showed that the nanocomposite with 1 wt% NPs had a more homogenized blend. 1 wt% TiO₂ nanocomposite exhibited a higher, but non-significant, impact strength compared to the controls. ANOVA showed significant differences in the impact and flexural strengths between nanocomposites with various contents of TiO2 NPs.

Conclusion. The nanocomposite with 1 wt% TiO2 NPs exhibited fewer micro-pores and micro-cracks in the SEM crosssections. A non-significant increase was also observed in the impact strength with TiO₂ NPs at 1 wt%. Further increase in TiO₂ NPs decreased both the impact and flexural strengths. The compressive strength of the heat-cured acrylic resin was not affected by the incorporation of NPs.

Influence of addition of zirconia on PMMA: A systematic review

The objective of this systematic review is to evaluate the effect of the incorporation of zirconia (ZrO₂) particles on the mechanical properties of PMMA (polymethyl methacrylate), and to establish which characteristics of this material yield the best results aiming their biomedical applicability. This study was carried out in accordance with the Items of Preferred Reports for Systematic Reviews and Meta-Analyzes (PRISMA) and is registered in PROSPERO under registration number: CRD42018095801. The searches were carried out in the PubMed, MEDLINE, Scopus and Cochrane Library databases for articles published up until April 2018. After the different stages of the article selection process, eight articles were selected for qualitative and quantitative analysis. All were in vitro studies, totaling 536 evaluated samples. The concentrations of zirconia ranged from 0.5% to 20% and the particle sizes were between 15 nm and 10 μm. The incorporation of zirconia particles did not increase the flexural strength of PMMA in only one study. While the concentration of zirconia influences PMMA, the type of acrylic resin, size, and silanization of zirconia particles did not influence the results. Thus, the addition of zirconia particles showed a positive effect on PMMA enhancing their use in the medical and dental field, especially when certain anatomical areas requires higher strength of the materials, providing longevity for the rehabilitation.

The effect of incorporating various reinforcement materials on flexural strength and impact strength of polymethylmethacrylate: A meta-analysis

Polymethylmethacrylate (PMMA) is a widely used denture base material with a major drawback of inferior mechanical properties. In the existing published reports, most studies indicate the superiority of the incorporation of various reinforcement materials in PMMA in terms of the flexural strength (FS) and impact strength (IS), whereas none shows the compilation and comparison of all. The present meta-analysis aims at synthesizing all the available data. The purpose of this study was to systematically review the existing reports to compare and evaluate the effect of various reinforcement materials on FS and IS of heat-cured acrylic resin (PMMA) by combining the available evidence in a meta-analysis. A search strategy was adopted using PubMed, ScienceDirect, Ebscohost, Google Scholar, and Cochrane Central Register of Controlled Trials in February 2018 to screen research studies. These studies were screened against predetermined criteria for eligibility for meta-analysis. In the present meta-analysis, twenty articles were included. Out of 15 data available on reinforcement, 14 showed better results for IS of reinforced PMMA resin as compared to their respective control group. Out of the 25 available data, 11 showed better results for FS of reinforced PMMA resin when compared to their respective control group. The homogeneity test of meta-analysis confirmed acceptable heterogeneity among 15 reinforcement techniques of IS (i² = 95.8%) and 25 reinforcement techniques of FS (i² = 96.2%). A random-effects model and fixed-effects model were used for analysis. The present meta-analysis showed that reinforcement of PMMA can significantly increase FS and IS. Hence, it can be incorporated in clinical practice.

A Comparison of the Flexural and Impact Strengths and Flexural Modulus of CAD/CAM and Conventional Heat-Cured Polymethyl Methacrylate (PMMA)

PURPOSE

The introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) technology to the field of removable prosthodontics has recently made it possible to fabricate complete dentures of prepolymerized polymethyl methacrylate (PMMA) blocks, which are claimed to be of better mechanical properties; however, no published reports that have evaluated mechanical properties of CAD/CAM PMMA. The purpose of this study was to compare flexural strength, impact strength, and flexural modulus of two brands of CAD/CAM PMMA and a conventional heat-cured PMMA.

MATERIALS AND METHODS

45 rectangular specimens (65 mm × 10 mm × 3 mm) were fabricated (15 CAD/CAM AvaDent PMMA specimens from AvaDent, 15 CAD/CAM Tizian PMMA specimens from Shütz Dental, 15 conventional Meliodent PMMA specimens from Heraeus Kulzer) and stored in distilled water at (37  ± 1°C) for 7 days. Specimens (N = 15) in each group were subjected to the three-point bending test and impact strength test, employing the Charpy configuration on unnotched specimens. The morphology of the fractured specimens was studied under a scanning electron microscope (SEM). Statistical analysis was performed using one-way ANOVA and Tukey pairwise multiple comparisons with 95% confidence interval.

RESULTS

The Schütz Dental specimens showed the highest mean flexural strength (130.67 MPa) and impact strength (29.56 kg/m² ). The highest mean flexural modulus was recorded in the AvaDent group (2519.6 MPa). The conventional heat-cured group showed the lowest mean flexural strength (93.33 MPa), impact strength (14.756 kg/m² ), and flexural modulus (2117.2 MPa). Differences in means of flexural properties between AvaDent and Schütz Dental specimens were not statistically significant (p > 0.05).

CONCLUSIONS

As CAD/CAM PMMA specimens exhibited improved flexural strength, flexural modulus, and impact strength in comparison to the conventional heat-cured groups, CAD/CAM dentures are expected to be more durable. Different brands of CAD/CAM PMMA may have inherent variations in mechanical properties.

Antibacterial activity, cytotoxicity and mechanical behavior of nano-enhanced denture base resin with different kinds of inorganic antibacterial agents

Silanized aluminum borate whiskers (ABWs) of 4 wt%, silanized zirconium dioxide nanoparticles (nano-ZrO₂) of 2 wt% were mixed with polymethyl methacrylate (PMMA) powder to get ZrO₂-ABWs/PMMA composites. Titanium dioxide (TiO₂), silver-supported titanium dioxide (Ag/TiO₂), silver-supported zirconium phosphate (Novaron) and tetrapod-like zinc oxide whiskers (T-ZnOw) antibacterial agents of 3 wt% were mixed with ZrO₂-ABWs/PMMA composites respectively to fabricate standard specimens. Plaque biofilms on the specimens surface were investigated for colony-forming units (CFUs). In addition, cytotoxicity and mechanical behavior were evaluated. Results showed that the CFUs values of S. mutans and C. albican biofilms on the four antibacterial composites surface were all reduced (p<0.05) compared to the blank and control groups. The antibacterial composites did not have an adverse effect on fibroblast growth in this study (p>0.05) except TiO₂ and Ag/TiO₂ groups of undiluted extracts. The flexural strength and surface hardness of Novaron and T-ZnOw groups were increased (p<0.05) compared to the control group.

PMMA denture base material enhancement: a review of fiber, filler, and nanofiller addition

This paper reviews acrylic denture base resin enhancement during the past few decades. Specific attention is given to the effect of fiber, filler, and nanofiller addition on poly(methyl methacrylate) (PMMA) properties. The review is based on scientific reviews, papers, and abstracts, as well as studies concerning the effect of additives, fibers, fillers, and reinforcement materials on PMMA, published between 1974 and 2016. Many studies have reported improvement of PMMA denture base material with the addition of fillers, fibers, nanofiller, and hybrid reinforcement. However, most of the studies were limited to in vitro investigations without bioactivity and clinical implications. Considering the findings of the review, there is no ideal denture base material, but the properties of PMMA could be improved with some modifications, especially with silanized nanoparticle addition and a hybrid reinforcement system.